When I bought this I thought FTP server is included by default, but it seem its not. Now I want to do that i.e I want that all users and all shared files an be reached from outside network just like from local network. Now I understand that samba can do this and I tried to find solution in official samba guide:

But this guide is so big and complex that a noob like me just gets confused. So please can you help me?
I want only these solutions.

1) you can mount a network drive with your user/pass from anywhere outside your local network and it will be displayed in widows as network drive, just like in local network
2) normal windows ftp program can be used to access my files (for example cute-FTP)

If you want to access your drive from outside the local network then Samba is not the best solution.

Since you have ssh up and running, you actually already have a secure FTP server ready to use; sshd has a built in server. You'll need a secure FTP client to connect. I'm not sure about cute-FTP but I believe FileZilla can be used if you want something graphical, and there's a command line based program, psftp, which comes with PuTTY.

So if you can connect with ssh/PuTTY from outside your network then you can connect with SFTP. To do this you just need to setup port-forwarding on your router for port 22. Your router setup might refer to this as Network Address Translation or NAT. This ensures that any packets from the internet to <your.external.ip.address>:22 are re-directed to <192.168.internaladdress.ofmywd>:22.

You probably want to look at a service such as www.no-ip.com or dynDNS to ensure you have a consistent way of finding your IP address in the outside world too.

I managed to get inside with sftp but problem is that *everything is shared*. I want just a normal share, where user logs in with his account and sees only shared folders I've setupped for his acount. is this possible with built in server or do I have to install some other ftp program to my WD?